Plasma levels of false neurotransmitters across the brain in portal-systemic encephalopathy

Arterial and internal jugular venous levels of false neurotransmitters (FNTs: octopamine, OCT, and phenylethanolamine, PEA), aromatic and branched-chain amino acids, glutamine, ammonia, and pH were measured in patients with portal-systemic encephalopathy (PSE) and in appropriate controls to define the role of these parameters in the pathogenesis of hepatic coma. The typical plasma patterns reported in the literature were observed: hyperammonaemia (59 +/- 8 mumol/l v. controls 30 +/- 4, P less than 0.005), elevated OCT (19 +/- 3 nmol/l v. 6 +/- 1, P less than 0.001) and PEA (64 +/- 8 nmol/l v. 27 +/-3, P less than 0.001), high ratio of aromatic to branched-chain amino acids (0.92 +/- 0.12 v. 0.32 +/- 0.04, P less than 0.005), and variable glutamine levels 216-734 mumol/l). No consistent net flux into or out of the brain could be demonstrated for any of these substances. The degree of encephalopathy correlated with the level of respiratory alkalosis (r=0.325, P less than 0.05) which, in turn, correlated with the degree of elevation of plasma OCT (r=0.439, P less than 0.05) and PEA (r=0.489, P less than 0.05) as well as with the excess of glutamine efflux from the brain (r=0.927, P less than 0.05). These findings support current views that hyperammonaemia, plasma amino acid imbalance, and elevated production of FNTs are interrelated disturbances which contribute to the pathogenesis of PSE. In addition, the data suggest that alkalosis accentuates the altered metabolism of these substances within the brain.